1. Field of the Invention
The present invention relates to a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication device including a dielectric ceramic used at high frequencies such as microwaves and millimeter waves.
2. Description of the Related Art
Dielectric ceramics used at high frequencies such as microwaves and millimeter waves are widely used for dielectric resonators, circuit boards, and the like.
A dielectric resonator has a configuration in which copper plating conductors are disposed on a dielectric ceramic. When a metallic coating for providing such copper plating conductors is not tightly joined to the dielectric ceramic, cavities are formed at the interface between the metallic coating and the dielectric ceramic, thus creating a large energy loss and thereby failing to increase the Q factor of the dielectric resonators.
In order to increase the adhesive strength to the metallic coating, the dielectric ceramic undergoes an etching process in general. A technique for improving etching properties is disclosed in Japanese Unexamined Patent Application Publication No. 5-315821. This technique is hereinafter referred to as a first related art.
The first related art relates to a technique for forming a copper coating on a ZrO2xe2x80x94SnO2xe2x80x94TiO2 ceramic. In the first related art, cobalt oxides are added to ceramic materials in an amount of 2-20% by weight, and the mixture is then fired to form a sintered ceramic having cobalt oxide deposits thereon, thereby improving the etching properties. The cobalt oxide deposits are then removed by an etching process to make the ceramic surface rough, thereby increasing the adhesive strength to the copper coating.
Alternatively, the following technique is disclosed in Japanese Unexamined Patent Application Publication No. 8-335810. A ceramic surface is uniformly made rough by an etching process to cause the surface to have a maximum roughness of 1.0-3.0 xcexcm, thereby obtaining superior plating properties. This technique is hereinafter referred to as a second related art.
However, in the first related art, since firing temperature and atmosphere for obtaining ceramics have significant effects on the deposition of the cobalt oxides, it is difficult to deposit a desired amount of cobalt oxides on a sintered ceramic. Therefore, there is a risk that a difference in adhesive strength to metallic coatings is large. Furthermore, since the amount of removed cobalt oxides varies depending on etching conditions for removing the cobalt oxides, there is a risk that a difference in adhesive strength to metallic coatings is large.
On the other hand, in the second related art, a ceramic surface can be made rough only when ceramics having superior etching properties are used. Thus, there is limitations on ceramic materials. That is, the second related art cannot be used for ceramics having inferior etching properties. Therefore, this art is not effective in obtaining, for example, a dielectric ceramic having a desired dielectric constant in some cases.
Accordingly, it is an object of the present invention to provide a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication device including a high-frequency dielectric ceramic used at high frequencies which solves the above problems.
In order to solve the above problems, a high-frequency dielectric ceramic used in the present invention contains a first ceramic having an adhesive strength of 70 newtons or more per 2 millimeter square to metallic coatings and a second ceramic having an adhesive strength of less than 70 newtons per 2 millimeter square to metallic coatings. In the composition of the high-frequency dielectric ceramic, the condition 10xe2x89xa6{A/(A+B)}xc3x97100 less than 100 is satisfied, wherein A represents the volume of the first ceramic and B represents the volume of the second ceramic.
The first ceramic preferably includes an MgOxe2x80x94TiO2 ceramic or a BaO-RemOnxe2x80x94TiO2 ceramic, where Re is at least one element selected from the group consisting of La, Pr, Ce, Nd, Sm, Gd, Er, and Y; m=2 and n=3 when Re is at least one element selected from the group consisting of La, Nd, Sm, Gd, Er, and Y; m=6 and n=11 when Re is Pr; and m=1 and n=2 when Re is Ce.
The second ceramic preferably includes at least one ceramic selected from the group consisting of a BaOxe2x80x94TiO2 ceramic, a SrOxe2x80x94TiO2 ceramic, an Al2O3 ceramic, a MgOxe2x80x94SiO2 ceramic, a ZrO2xe2x80x94TiO2 ceramic, a SnO2xe2x80x94TiO2 ceramic, a ZrO2xe2x80x94SnO2xe2x80x94TiO2 ceramic, and a Re2O3xe2x80x94Al2O3 ceramic, where Re is at least one selected from the group consisting of La, Nd, and Sm.
A high-frequency dielectric ceramic used in the present invention preferably has an average grain size of 10 xcexcm or less.
The present invention provides a dielectric resonator including the dielectric ceramic electromagnetically coupled to input/output terminals so as to function. In the dielectric resonator, the dielectric ceramic described above can be used at high frequencies and has copper plating conductors thereon.
The present invention provides a dielectric filter including the dielectric resonator described above.
The present invention provides a dielectric duplexer including at least two dielectric filters. In the dielectric duplexer, at least one of the dielectric filters includes the dielectric filter describer above.
The present invention provides a communication device including the dielectric duplexer described above, a transmitting circuit connected to an input portion of the dielectric duplexer, a receiving circuit connected to an output portion of the dielectric duplexer, and an antenna connected to an input/output portion of the dielectric duplexer.